1. Field of the Invention
The present invention relates to a bearing unit and a pivot device including the bearing unit.
2. Description of the Related Art
Conventionally, there is known a magnetic disk device including a bearing unit provided with a swing arm, in which bearings are multi-staged in accordance with multi-staging of magnetic disks for increasing storage capacity of a hard disk drive, whereby the bearing unit supports a plurality of magnetic disks. In the magnetic disk device as described above, there is known a technology for configuring the bearing unit with a plurality of bearings for supporting multi-staged arms (for example, see JP 2002-100128 A).
In a magnetic disk device of JP 2002-100128 A, a spacer is disposed between a first pivot and a second pivot including a sleeve supported with respect to a shaft through an intermediation of upper and lower two bearings, and an actuator block including a head suspension is fixed to each of the sleeve of the first pivot and the sleeve of the second pivot.
However, in the case of a double-row roller bearing as in the conventional structure, preload for ensuring rigidity is dispersed to two roller bearings, and hence a large load is applied to the roller bearings. Therefore, the roller bearings have a short life. Further, for example, in the case of a quadruple-row roller bearing of the bearing unit, due to expansion and contraction of an adhesive applied between each outer race of all four rolling bearings and the sleeve, and the influence of precision of the outer races and the sleeve fitted to each other, circularity of a rolling contact surface of each outer race changes. The change of circularity of the rolling contact surface of each outer race results in application of stress with respect to the rolling element and the rolling contact surface, thereby causing a problem of unstable resonance and wave torque.
The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a bearing unit having a long life and capable of stabilizing the torque and the resonance, and a pivot device including the bearing unit.